Drill grinding machine



y 27, 1952 H. F. B. HC5GFORS DRILL GRINDING MACHINE Filed Dec. 50, 1947 \NVENTOQ.

Patented May 27, 1952 umrao s TATES PATENT o FFieE Hans Sweden Application December 30, 1947, SerialiN'ofiT9L595 In Sweden February 23, 1946 Section 1, Public Law 690, :August 8., 194%; Patent expires February 23,1966

'4 Claims. (Cl. SI- 219") This invention relates to twist drill grinding machines.

The object of the invention is to provide a machine for grinding and sharpening twist drills that may be of avery simple and cheap construction and so easy to handle that it could be :used in every workshop where drills are to be sharpened.

For good results in drilling it is necessary that the apex of the drill point should substantially coincide with the geometric centre of the drill and that the two cutting edges should be ground with uniformity and exactness as to angularity and length thereof. With drills of large diameters it is also important that the cross edge forms a certain angle with the cutting edges. This cross edge which in twist drills for drilling in iron and steel with a point angle of 118 ought to be 55 is normally obtained by giving the tapered or clearing surfaces of the drill the shape of a cone, especially in machine grinding. This method has the disadvantage, however, that the angle between the edge and its tapered surface is unequal along the cutting edge, usually 6' at the periphery and about 26 at the tip. TIhus the cutting edge is not uniformly strong and is therefore first worn out at the centre.

Further characteristic features of the invention will appear from the following description of a preferred embodiment of a machine for grinding twist drills, which is illustrated in the accompanying drawing, in which Fig. vl shows a twist drill in side view.

Fig. 2 is a top view of Fig. 1.

Fig. 3 is a section on the line III-III in Fig. 1.

Fig. 4 is a plan view, partly in section, of the machine.

Fig. 5 is a front view of Fig. 4 partly in section.

Fig. 6 is a section on the line VI-VI of Fig. 4, and

Fig. 7 is a side view of Fig. 5.

Referring to the drawing, from the cutting edges la and I b inclined planes (clearance planes) 2a. and 2b are ground at a suitable angle a in order to obtain a cutting edge well resistant to wear. These planes intersect a plane coinciding with the axis of the drill and parallel with the edges la and lb along an intersection line 3a. If now another plane (cross edge plane) 4a or M; is ground inclining from the line 3: at an angle 1) the cross edge plane 4a forms with the clearance plane 21) a cross edge 5b, and correspondingly the plane 41) with the plane 2a a cross edge 5a, the two cross edges 5a and 5b in horizontal projection forming a straight line.

2 A calculation will showthatif the angle a is 6 the angle lb must be about '30 if the cross edge angle is to be 55'.

Apr'ferred embodiment of a-mac'hine for this grinding will now be described. A plate "I is intended to be secured to a grinding machine in suitable relation to a grinding wheel 2, Fig. 4, as will be described below. A stud '3 is secured to the plate I and extends upwards through a stand I. Slots '5 and 6 in the stand and a handle 1 make it possible to fix the stand in desired radial positions in relation to the stud. The plate fl has a projection 8 for holding the stand in a fixed position during the grinding operation. In the stand ii is a stationary shaft 9, which extends from the stand towards the grinding wheel 2. The outermost end of the shaft 9 is formed as a sector, one radius ll] of which is "horizontal and the other ll of which is vertical. The latter .is also in line with the front plane 12 of the grinding wheel 2 and the sector behind this plane I2.

Loosely mounted on the shaft 9 is a swing-arm 13 with two bushings I 4 and I5, the centre lines 16 and l1 of which are in the same plane and form .an angle d with each other which is equal to the half of the drill point angle.

The apex of the angle dis near the outer end of the shaft 9 when thebushing l4 contacts the stand I. 'The bushing '14 has a cam l8, one side of which is radial 'to the axis l6 and forms the angle (+a) to "the .plane formed by the centre lines 16 and I]. When the vplate l and stand 4 are fixed in position for grinding the radial part of cam I8 coincides with the front side 12 of the grinding wheel 2. On its underside the bushing H has another cam "[9, which is parallel to the axis I6 and cooperates with a roller 20 on a lever 24 pivoted on a shaft 22 rigidly connected on the stand 4. The .roller 20 is journalled on a pin 23 fast on the lever 2|. A link 24 is pivoted on a. pivot pin 25 on the lever 2| and has a slot 26 for a screw 2'1 (secured to the stand 4. A spring 28 one end 01' which is connected to the lever 21 and the other end to a screw 29 in the stand 4 gives the lever 2| a counter-clockwise movement, Fig. '7, so that the right hand end of slot 26 stops against the screw 21. The swing-arm I3 is turned downwards around the shaft 9 by it's own weight but is stopped in different positions when the cam 18 the roller 20 on the lever 21. In the just described position of the lever 2| the axis l1 forms the angle a with the horizontal plane. If the swing-arm is is pressed down (against the action of the spring 28) until 3 the left hand end of the slot 26 contacts the stud 21 the axis l1 inclines to the angle 22, Fig. 3, to the horizontal plane.

In the bushing i on swing-arm I3 is loosely mounted a socket 30, Fig. 4, having a flange 31 in which two notches 32 are placed exactly opposite each other. A catch 33 slidably mounted in the swing-arm I3 is held by a spring 34 in mesh with one of the notches 32 thus preventing the socket 30 from rotating around its axis H. At the opposite end of the socket a nut 35 is secured at some distance from the end of the bushing 15, and a spring-actuated pin 36, Fig. 6, pushes on the nut 35 thus causing the flange SI of socket 30 to contact the bushing 15.

The socket 30 is suitably adapted, for instance by means of a cone, for fastening the shank of a drill chuck 31 for a drill 38. On the outward side of the bushing IS an eccentric cam 39 is rigidly mounted on a shaft 40 pivoted both in the bushing and in a plate 4| screwed to the bushing. By a button 43 rigidly connected to the shaft 49 (for instance by a pin 42) the cam 39 can be turned so that it contacts the flange 3| of the socket 30 and pushes the socket towards the grinding wheel 2.

In utilizing the machine the stand 4 is fixed to the late I in such a position that it contacts the projection 8 and with the aid of a ruler the plate I is attached to the grinding machine so that the radial plane of the cam I8 of the swingarm l3 comes in line with the plane I2 of the grinding wheel 2. Then the handle 1 is loosened and the stand 4 is turned clockwise, Fig. 4, in order to permit insertion of a drill 38 in the chuck 31. Thereupon the swing-arm I3 is pushed ou wards on the shaft 9 so that the drill has free passage outside the shaft. After pushing the swing-arm I3 back again until it contacts the stand 4 the drill is adjusted so that one of its cutting edges is parallel to the apex of the planes Ill and H of the shaft 9 and touches the side ll of the sector, and the drill is then secured in the chuck. Then the stand 4 is turned to contact the projection 8 and is fixed in that position by the handle I.

If the swing-arm I3 is now pushed along the shaft 9 the drill comes into the path of the grinding wheel 2 and the clearance angle a of the drill is ground, if desired first after having pushed the drill towards the wheel by the aid of the button 43, which has a scale, for instance as shown in Fig. 6, with numbers according to which a oertain position of the button can be determined. The swing-arm I3 is pushed to and fro in order to avoid the grinding wheel being worn only at one point. During this movement the roller 29 rolls on the cam l9 and the swing-arm i3 by the action of the spring 28 is held in a position corresponding to the angle a. Then the button 43 is turned back to its inoperative position through which the socket 30 is pushed away from the grinding wheel by the spring-actuated pin 36. Then the swing-arm I3 is swung downwards until the left hand end, Fig. 7, of the slot 26 in link 24 stops against the stud 21, and the swing-arm I3 is again pushed to and fro on the shaft 9, by which the angle 1), Fig. 3, is ground on the drill. Also during this to and fro motion the drill is pushed against the grinding wheel by successively turning the button 43 until it reaches the same position of the scale number as determined in the foregoing grinding of angle a. Now the button 43 is turned back again to its original position and the swing-arm I3 is pushed outwards so that the drill comes into the space between the shaft 9 and the grinding wheel 2 thus giving the drill room to turn around its axis 11. This is effected by grasping the nut 35 and turning the socket 30 until the catch 33 falls into the opposite notch 32. The drill is thus turned and the same procedure as just described is repeated for grinding the second cutting edge of the drill, keeping especially in mind that the button 43 must always be turned to the same degree of the scale as was first determined.

It is obvious that if the cam 39 has a very little eccentricity, for instance only a hundredth of an inch, a graduation on it only in tenths of a revolution, 1. e., thousandths of an inch, gives a very good accuracy causing the apex of the drill to be as near as possible in accordance with the geometric centre. Since the stand 4 is fixed during the grinding procedure the angle d, Fig. 4, must be the same at both cutting edges of the drill, which, as before mentioned, is of very great importance. I

After the grinding is finished the stand 4 is loosened from the stud 3 and swung out in order to remove the ground drill and fit the next one to be ground. The resulting shape of the point of the drill is shown in Figs. 1 and 2.

Different modifications may be made in the device shown and described without departing from the scope of the invention. Thus other devices than the lever ZI and the link 24 may be used in order to obtain the angles a and I). Also the link I4 and the stud 21 can be equipped with screws in order to obtain other angles a and b than those determined above. The swin -arm 13 also can be made in two parts, the relative position to one another of which can be altered for obtaining another angle d, Fig. 4, i. e. a more acuteor obtuse-angled drill point.

Having now described my invention, what I claim as new and desire to secure by Letters Patent is:

l. A device for grinding twist drills comprising in combination a shaft, a grinding wheel, a drill holder and a support carrying the shaft, the axis of which coincides with the face plane of the grinding wheel, said shaft in its turn carrying the drill holder in such position that the axis of an inserted drill cuts the axis of the shaft, said drill holder being rotatable on said shaft and also movable alongside the face of said grinding wheel, an alining edge on said support for adjusting the cutting edge of the drill into alinement With the axis of said shaft, said alining edge coinciding with the axis of said shaft and being adjustable to coincide also with the face of said grinding wheel, in which position said support is fixed during the grinding operation, and means for setting the drill holder at different predetermined angles relative to the grinding Wheel.

2. A device for grinding twist drills comprising in combination a shaft, a grinding wheel, a drill holder and a support carrying the shaft, the axis of which coincides with the face plane of the grinding wheel, said shaft in its turn carrying the drill holder in such position that the axis of an inserted drill cuts the axis of the shaft, said drill holder being rotatable on said shaft and also movable alongside the face of said grinding wheel, said shaft at the point where the axis of the drill cuts the axis of the shaft being formed as a sector with its tip in the axis of the shaft and with one radius parallel to the face of said grinding wheel, and means for set- 5 ting the drill holder at different predetermined angles relative to the grinding wheel.

3. A device for grinding twist drills comprising, in combination a shaft, a grinding wheel, a drill holder and a support carrying the shaft, the axis of which coincide with the face plane of the grinding wheel, said shaft carrying an arm which in its turn carries the drill holder in such position, that the axis of an inserted drill cuts the axis of the shaft, said drill holder being adjustable around the point where the axis of the drill cuts the axis of said shaft to different angles between said two axes, said shaft having a cut off portion facing towards said grinding wheel, said portion forming a sector with its tip in the axis of said shaft and one radius parallel to said grinding wheel, and means for setting said drill holder at different predetermined angles relative to the grinding wheel.

4. A device for grinding twist drills comprising, in combination a shaft, a grinding wheel, a drill holder and a support carrying the shaft the axis of which coincides with the face plane of the grinding wheel, said shaft in its turn carrying the drill holder in such position that the axis of an inserted drill cuts the axis of the shaft, said drill holder being rotatable on said shaft and also movable alongside the face of said grinding wheel, means for feeding the chuck 6 with the drill against the grinding wheel, an alining edge for adjusting the cutting edge of the drill into alinement with the axis of said shaft, said alining edge coinciding with the axis of said shaft and being adjustable to coincide also with the face of said grinding wheel, in which position said support is fixed during the grinding operationyand means for setting said drill holder at different predetermined angles relative to the grinding wheel.

HANS FREDRIK BIRGER HiU'GFORS.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 584,114 Hill June 8, 1897 607,306 Walker July 12, 1898 819,173 Schmaltz May 1, 1906 1,467,491 Oliver Sept. 11, 1923 1,524,672 Rabut Feb. 3, 1925 1,576,311 Des Jardins Mar. 9, 1926 2,193,186 Bannister Mar. 12, 1940 2,202,819 Yantiss June 4, 1940 2,232,563 Schumacher Feb. 18, 1941 2,328,549 Eich et a1, Sept. 7, 1943 

